Electrographic oscillograph

ABSTRACT

An electrographic oscillograph includes a linear corona source generally aligned with a narrow exit slit that is positioned between the source and a narrow control slit formed by two knife edges which, in turn, is arranged at an angle to the exit slit. An input signal to be recorded is impressed across the knife edges and produces an electrical field which causes deviation of the ion stream which will then pass through the control slit at different points along its length in accordance with the amplitude of the input signal. The oscillograph can be made light responsive by coating one knife edge with a photoconductor so that an electrostatic field is produced which will vary in response to the illumination incident on the knife edge.

United States Patent [72] Inventor Lee F. Frank Rochester, NY.

[21] Appl. No. 854,819

[22] Filed Sept. 3, 1969 [45] Patented Oct. 5, 1971 [73] Assignee Eastman Kodak Company Rochester, N.Y.

[54] ELECTROGRAPHIC OSCILLOGRAPH 6 Claims, 5 Drawing Figs.

[52] U.S. Cl 346/74 ES, 250/495 GC, 313/63, 313/80, 313/82 NC, 313/83, 317/4, 346/74 EB [51] Int. Cl Gold 9/04, HOlj 37/08 [50] Field of Search 346/74 ES, 74 EB; 250/495 GC, 49.5 ZC; 178/6.6 A; 313/63, 80,82 NC, 83; 317/4 [56] References Cited UNITED STATES PATENTS 2,771,336 11/1956 MacGriff 178/66 A Primary Examiner-Terrell W. Fears Assistant Examiner-Howard W. Britton Attorneys-William H. J. Kline, Paul R. Holmes and Lloyd F.

Seebach ABSTRACT: An electrographic oscillograph includes a linear corona source generally aligned with a narrow exit slit that is positioned between the source and a narrow control slit formed by two knife edges which, in turn, is arranged at an angle to the exit slit. An input signal to be recorded is impressed across the knife edges and produces an electrical field which causes deviation of the ion stream which will then pass through the control slit at different points along its length in accordance with the amplitude of the input signal. The oscillograph can be made light responsive by coating one knife edge with a photoconductor so that an electrostatic field is produced which will vary in response to the illumination incident on the knife edge.

PATENTEUUCT 519m SHEET 1 0F 2 LEE F. FRANK mvsmon BY AGE/VT FIG. 2

PATENTEUUBT 5197! 3511.414

SHEET 2 UF 2 Illulllllld 3 EE/ZNIOKV) 28 (/OOV.) L. 25 26 29(30 Wfi' 2/ LEE F. FRANK INVEN'IOR Mala ax AGENT ELEC'I'ROGRAPHIC OSCILLOGRAPH FIELD OF THE INVENTION invention relates to an electrographic oscillograph and more particularly to an oscillograph which operates by deviation of an ion stream passing from an ion source to a recording member wherein such deviation corresponds in frequency and amplitude to that of an input signal.

DESCRIPTION OF THE PRIOR ART Prior art systems for obtaining permanent records of electrical signals have generally taken either of two forms. In one form, the signal is displayed on the screen of a cathode ray oscilloscope from which a permanent recording can be obtained by well known methods. One such method is by imagewise exposure of a photoconductive material by the displayed signal. Another method is by use of a special pin-faced cathode-ray tube by which a charge image generated on the face by the electron beam is transferred to a recording paper. Such systems, using a cathode-ray tube, are capable of highfrequency response but are relatively expensive.

In a second form, an electrical signal is used to drive a recording am through suitable means, such as a dArsonval galvanometer movement. The arm can carry either a pen point for making a direct image in ink, or a needle point to which is applied a high electric potential. In the latter system, the spark discharge through a record member to a grounded backing electrode produces either a pattern of holes corresponding to the input signal, if the record member is a paper sheet, or a charge pattern on the surface of the member if it is an insulator coated paper. In either the photographic or the direct print process, the frequency response of the oscillograph is limited by the inertia of the writing means.

In general, the use of a corona discharge in an electrographic process has involved controlled transmission of the corona by providing field-free regions which block transmission of the corona. The field-free regions correspond to the image and produce a charge image on a receiving sheet. The fact that low field areas are involved in producing the image has led to low time frequency response and a reduction in spatial resolution due to diffusion of the ion stream. If the ion stream is modulated by deflecting it in a region of relatively high field and directing it through a slot, there need not be any low field area in the ion stream path and, consequently, the transit time is short. The reduction in transit time improves time frequency response and greatly reduces the effect of diffusion on spatial resolution.

. SUMMARY OF THE INVENTION The principal object of the invention is to provide a simple electrographic oscillograph having a frequency response extending to many kilocycles per second.

A further object of the invention is to provide an electrographic oscillograph in which the structure of the writing head is such that no moving parts are required thereby decreasing the effective inertia of the writing head and reducing its cost.

A still further object of the invention is to provide an oscillograph in which a controlled corona discharge produces an ion stream which is responsive in frequency and amplitude to that of an input signal for recording said signal on a suitable recording medium.

These and other objects and advantages of the invention will be apparent to those skilled in the art by the description which follows.

The objects of the invention are attained by mounting a linear ion source within a dielectric housing or chamber that is provided with an elongated slit arranged generally parallel to the ion source, at least a portion of each edge of the slit being conductive. A pair of closely spaced planar electrodes are arranged to form a second slit which is arranged at a small acute angle to the elongated slit and in closely spaced relation thereto. A dielectric recording medium is positioned upon a metal plate which is substantially parallel to the planar electrodes and also in closely spaced relation thereto. Ions generated by the ion source can pass directly through both slits to the dielectric receiving sheet only at the intersection of the slits. When an input signal is applied to the planar electrodes, the flow of ions is deviated in response to the input signal. Since the flow of ions can reach the receiving sheet only after passing through both slits, the transverse displacement of the How relative to the receiving sheet is in accordance with the amplitude of the input signal and the longitudinal displacement is in accordance with the frequency of the input signal.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective representation of the writing head of an electrographic oscillograph in accordance with the invention;

FIGS. 2 and 3 are sectional views taken along the lines 22 and 3-3, respectively, of FIG. 1;

FIG. 4 is a schematic representation of an alternative embodiment of the invention; and

FIG. 5 is an equivalent circuit of the embodiment of the invention shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a linear corona source, generally designated by the numeral 1, comprises a corona wire 2 electrically mounted within a dielectric housing 3 which is provided with an elongated slit 4 which is generally parallel to, aligned with and spaced from corona wire 2. A pair of planar knife edge electrodes 5 and 6 is arranged below slit 4, the electrodes being arranged relative to each other so as to define a slit 7. The electrodes 5 and 6 are located in close proximity to and are generally parallel to that portion or side of housing 3 in which the elongated slit 4 is formed. Slit 7 extends in the same general direction as slit 4 and is arranged at a small acute angle thereto so that the two slits intersect (when viewed from the position of wire 2) at about the midpoint of slit 4. An electrically conductive metal plate 8 is disposed in close proximity to and generally parallel to electrodes 5 and 6, said plate supporting an electrographic receiving sheet 9 on which a trace of an input signal will be recorded.

A typical biasing circuit is also shown schematically in FIG. 1. Corona wire 2 is maintained at a potential of approximately 15,000 volts with respect to ground by a source generally designated by the numeral 10. A potential of about 250 volts with respect to ground and designated by numeral 12 is connected to portion 11, electrode 5 being maintained at ground potential. Plate 8 is also maintained at a potential of about 250 volts with respect to ground by a source designated by the numeral 13. The input signal is applied at terminals 14 and 15 directly to electrodes 5 and 6, respectively.

With no input signal, that is, no voltage applied to terminals 14 and 15, the flow of ions 16 from corona wire 2 will be transmitted directly through slit 4 and will impinge upon electrodes 5 and 6 as best shown in FIG. 2A, except at that portion or point of slit 7 which lies directly under (intersects) slit 4. At such point, a portion of the flow of ions 16 will pass through slit 7 and impinge upon receiving sheet 9 as shown in FIG. 3A. When an input signal is applied to terminals 14 and 15, the flow of ions 16 will be deflected after passing through slit 4 and a portion thereof will pass through a different part of slit 7 in accordance with the amplitude and frequency of the applied signal. As a result, the flow of ions 16 is along the full length of slit 4 but the portion of flow of ions that can pass through slit 7 is determined by the input signal applied to terminals 14 and 15 and in accordance with the changes in am plitude and frequency. This can best be seen in FIGS. 28 and 38 where with an input signal (voltage on) the flow of ions 16.

cannot pass through slit 7 (FIG. 38) because it is deflected to the right and generally blocked or masked by electrode 6. However, a portion of the fiow of ions 16 as shown in FIG. 28 will not be blocked but will pass through slit 7 and impinge upon receiving sheet 9.

In actual operation, the deflection of the flow of ions should not be limited by any frequency up to at least 200 kilocycles per second. The frequency response of the oscillograph will be limited to the maximum writing rate that can be achieved with the concentrated corona source 1. The writing rate of the oscillograph as calculated from stationary measurements of the current density of the flow of ions 16 in writing areas can be to 100 inches per second. The flow of ions 16 can move across the receiving sheet 9 at such a rate that a sufficient charge cannot be placed on the receiving sheet 9. As a result, a visible image will not result upon development. It has been found that, for example, satisfactory results can be attained if the frequency is about 2 or 3 kilocycles per second and the receiving member.9 is moved at a rate of -2 to 3 inches per second. However, this example is merely illustrative and is not meant to indicate any limitation of the invention described herein.

For simplicity, the vertical separations between the linear corona source 1, electrodes 5 and 6 and receiving sheet 9 have been exaggerated in FIG. 1. In actual practice, the distance from slit 4 (bottom of housing 3) to receiving sheet 9 is less than one-eighth of an inch. Moreover, the deflection of the ion beam is not a linear function of voltage when straight slits are utilized in the writing head. By'introducing a slight curvature into slit 4 or slit 7, a linear response can be achieved. By other suitable designs of slits 4 and 7, any desired nonlinear response, such as a logarithmic response, can be achieved over a restricted range.

Another embodiment of the invention is shown in FIG. 4 wherein variations in illumination on a photoconductive material create a light dependency in the corona current transmitted through slits 4 and 7 of the writing head. Addi tional jaws and 21 formed by an electrically nonconductive material are positioned between slit 4 in housing 3 and electrodes 5 and 6, as shown in FIG. 4. The knife edges 22 and 23 of jaws 20 and 21, respectively, form a slit 24 which is generally parallel to, aligned with and slightly wider than slit 4. The surface of jaw 20 that faces slit 4 is coated with a photoconductive material 25 while the other surface is coated with a semiconductive material 26. The surfaces of jaw 21 are also coated with the semiconductive material 26.

FIG. 5 shows an equivalent circuit that corresponds to the embodiment of the invention shown in FIG. 4. Corona wire 2 is maintained at a potential of about 10,000 volts with respect to ground by means of a source 27. Plate 8 is connected directly to ground. Portion 1 1 of chamber 3 is at a potential of about 330 volts, while electrodes 5 and 6 are at a potential of about 100 volts. The surfaces of jaws 20 and 21 facing slit 4 are at a potential of about 230 volts while the other surfaces of jaws 20 and 21 are at a potential of about 200 volts, the potentials being derived from sources 28-31. The photoconductive and semiconductive coatings on jaws 20 and 21 are shown as a voltage divider system with the photoconductive material shown as a variable resistor. In the unilluminated state, the photoconductive material has a greater resistance than the semiconductor material and thus the potential impressed across the combination of the two materials appears substantially across the photoconductive material. Knife edge 22 of jaw 20 will then be a lower potential than knife edge 23 of jaw 21. When the photoconductive material is illuminated, the voltage across the photoconductive material drops to essentially zero and the potential impressed across jaw 20 appears across the semiconductive material. Knife edge 22 of jaw 20 will then be at a higher potential than knife edge 23 of jaw 21. Thus, in the unilluminated state the ion bean will bend towards jaw 20 and away from jaw 21. In the illuminated state, the ion beam will be bent away from jaw 20 and towards jaw 21. Depending upon the various positions and depending upon whether there is a constant bias voltage between the two knife edges 22 and 23, the flow of ions 16 will be deviated onto or off of the slit 7 in the electrodes 5 and 6, as the light impinging upon the photoconductive material varies in intensity.

Because of the addition of jaws 20 and 21 between slit 4 and slit 7, the mechanical adjustment of knife edges 22 and 23 can become critical. This positioning can be compensated for by using a low-impedance semiconductive material as the metallic connectors of knife edges 22 and 23, and then establishing potentials between the knife edges to twist the ion bean into alignment. It should also be noted that reversing the photoconductive material and semiconductive material on jaw 20, as shown in FIG. 4, will cause the ion beam to be deflected in the opposite direction both before and after illumination of the photoconductive material.

While the description of the invention has been with respect to preferred embodiments thereof, it will be understood that variations and modifications can be efiected within the spirit and scope of the invention as described above.

I claim:

1. Apparatus for recording a graphic representation of an input signal of variable amplitude and frequency on a recording medium in the form of a latent electrostatic charge image, comprising:

means for generating a generally continuous flow of ions and having a first elongated, generally linear slit through which said flow of ions is directed toward said recording medium;

electrode means arranged between and in spaced relation to said generating means and said recording medium and forming a second elongated, generally linear slit in a plane generally parallel to that of said first slit and angularly disposed relative to the midpoint thereof, said electrode means being responsive to said input signal for controlling the displacement of said flow of ions relative to said second slit in accordance with the amplitude and frequency of said input signal;

a source of potential connected to said generating means and said electrode means for establishing an electrostatic field in the region therebetween; and

means for applying said input signal to said electrode means for modulating said electrostatic field to displace said flow of ions relative to said second slit whereby only a portion of said flow of ions passes through said second slit to said recording medium, as determined by the amplitude and frequency of said input signal.

2. Apparatus as in claim 1 wherein said generating means comprises a housing defining said first elongated, generally linear slit, at least the edges of which are electrically conductive, and a corona source arranged within said housing and generally aligned with said first slit.

3. Apparatus as in claim 2 wherein said electrode means comprises a pair of planar electrodes, the facing edges of which form said second elongated, generally linear slit arranged at a slight angle to said first slit.

4. Apparatus as in claim 3 wherein said electrode means include a second pair of electrodes positioned between said pair of planar electrodes and the portion of said housing provided with said first slit, said second pair of electrodes defining a third slit slightly wider than either of said first and second slits and generally parallel to said first slit.

5. Apparatus as in claim 4 wherein said second pair of electrodes includes photoconductive means responsive to an input signal of variable light intensity.

6. Apparatus as in claim 5 wherein said photoconductive means comprise a layer of photoconductive material on at least a portion of one longitudinal edge of said wider slit and a layer of semiconductive material covering at least the reminaing portions of said same slit. 

1. Apparatus for recording a graphic representation of an input signal of variable amplitude and frequency on a recording medium in the form of a latent electrostatic charge image, comprising: means for generating a generally continuous flow of ions and having a first elongated, generally linear slit through which said flow of ions is directed toward said recording medium; electrode means arranged between and in spaced relation to said generating means and said recording medium and forming a second elongated, generally linear slit in a plane generally parallel to that of said first slit and angularly disposed relative to the midpoint thereof, said electrode means being responsive to said input signal for controlling the displacement of said flow of ions relative to said second slit in accordance with the amplitude and frequency of said input signal; a source of potential connected to said generating means and said electrode means for establishing an electrostatic field in the region therebetween; and means for applying said input signal to said electrode means for modulating said electrostatic field to displace said flow of ions rElative to said second slit whereby only a portion of said flow of ions passes through said second slit to said recording medium, as determined by the amplitude and frequency of said input signal.
 2. Apparatus as in claim 1 wherein said generating means comprises a housing defining said first elongated, generally linear slit, at least the edges of which are electrically conductive, and a corona source arranged within said housing and generally aligned with said first slit.
 3. Apparatus as in claim 2 wherein said electrode means comprises a pair of planar electrodes, the facing edges of which form said second elongated, generally linear slit arranged at a slight angle to said first slit.
 4. Apparatus as in claim 3 wherein said electrode means include a second pair of electrodes positioned between said pair of planar electrodes and the portion of said housing provided with said first slit, said second pair of electrodes defining a third slit slightly wider than either of said first and second slits and generally parallel to said first slit.
 5. Apparatus as in claim 4 wherein said second pair of electrodes includes photoconductive means responsive to an input signal of variable light intensity.
 6. Apparatus as in claim 5 wherein said photoconductive means comprise a layer of photoconductive material on at least a portion of one longitudinal edge of said wider slit and a layer of semiconductive material covering at least the reminaing portions of said same slit. 